Running costs updated 1 October 2026. Every electricity figure on this page is costed at the Ofgem price cap average electricity unit rate of 26.32p per kWh, which applies from 1 October to 31 December 2026. Your own tariff may be higher or lower, so check your latest bill before relying on these numbers.
However carefully you balance the chemicals, hot tub water eventually becomes "tired". Dissolved solids, body oils and chemical residues build up until sanitiser stops working well. This guide explains how often to change it, and how to tell when it is due.
Always follow your manual. This guide gives general UK guidance, drawn from manufacturers' instructions and standard water-care practice. It is not a substitute for your hot tub's own manual or for a qualified electrician. Where the two disagree, your manufacturer's instructions win.
The short answer
For most UK inflatable hot tubs, every one to three months, depending on how much you use it. Change it sooner if it stays cloudy, foams or smells after shocking.
A quick formula
A widely used industry rule is: water volume in US gallons ÷ 3 ÷ average number of bathers per day = days between changes. In litres, that works out as:
Litres ÷ 11.4 ÷ average bathers per day = days between changes
| Tub volume | 1 bather a day | 2 bathers a day | 4 bathers a day |
|---|---|---|---|
| 600 litres | About 53 days | About 26 days | About 13 days |
| 800 litres | About 70 days | About 35 days | About 18 days |
| 1,000 litres | About 88 days | About 44 days | About 22 days |
It is a rule of thumb, not a precise measurement. Heavy use, parties and poor showering habits shorten it.
Signs it is time to change the water
- Cloudy water that does not clear after shocking and a filter clean.
- Foam that keeps coming back.
- A strong chemical smell. That usually means chloramines (used-up chlorine), not too much chlorine.
- Readings that will not stay in range however you adjust them.
- Skin or eye irritation.
How to drain and refill
- Switch off and unplug the pump.
- Drain through the drain valve with a hose to a suitable drain. Do not run chemically treated water onto ponds or watercourses.
- Wipe the liner with a soft cloth and a spa-safe cleaner, then rinse.
- Clean or replace the filters.
- Refill, rebalance and reheat. See how to set up an inflatable hot tub for heat-up times and costs.
The cost of a refill
Each refill costs you water (an 800-litre tub is 0.8 cubic metres, so check your supplier's metered rate), a fresh dose of chemicals and the electricity for a full heat-up. That is about 26 kWh, or around £6.86 at 26.32p per kWh, before heat losses. Good water care stretches the time between refills, and that is where the saving is. See hot tub chemicals for beginners.
How to make the water last longer
- Shower before you get in, without soap residue or moisturiser.
- Rinse the filter weekly and rotate two filters.
- Keep the lid on whenever the tub is not in use.
- Shock after busy sessions.
- Use a hose pre-filter when filling.
Thinking about winter? Read should you leave a hot tub empty over winter?
The BestPicks UK hot tub guides
Choosing one
- Hot tub buying guide
- Are inflatable hot tubs worth it?
- Lay-Z-Spa vs CleverSpa
- Inflatable vs hard-shell hot tub
- How long an inflatable hot tub lasts
Setting up
- What to put under an inflatable hot tub
- How to set up an inflatable hot tub
- Hot tub accessories worth buying
Running and looking after it
- How much a hot tub costs to run
- Hot tub chemicals for beginners
- Should you empty a hot tub over winter?
- Using a hot tub in freezing weather
Compare models in our best hot tubs UK guide, or work out your bill with the hot tub running cost calculator.
Frequently asked questions
How often should you change the water in an inflatable hot tub?
Typically every one to three months, depending on use. A family using it daily will be at the shorter end.
Can I just top up the water instead of changing it?
Topping up replaces water lost to evaporation and splashing. It does not remove the dissolved solids that build up, so you still need full changes.
Where can I drain hot tub water in the UK?
Usually to a foul or combined drain, such as an outside gully. Do not drain treated water into ponds, streams or surface-water drains. Let chlorine levels fall first if you can, and check with your water company if unsure.
Why does my hot tub smell of chlorine?
A strong smell usually means used-up chlorine (chloramines), not too much. Shocking the water normally clears it. If it keeps returning, change the water.
